BLM LIBRARY 88057135 Technical Note 398 A Mass Spectrometer Method for Determining Percent-Range IHeiium in Gaseous Mixtures By Philip W. Holland November 1996 U.S. Department of the Interior Bureau of Land Management y^ IcrAQI U^ Bureau of Land Management Technical Note 398 A Mass Spectrometer Method for Determining Percent- Range Helium in Gaseous Mixtures by Philip W, Holland .^^ ,^ November 1996 BLM/HE/ST-97/001+37 00 CONTENTS Page Abstract 1 Acknowledgment 2 Introduction 2 Mass spectrometer system 3 Experimental procedures 8 Accuracy of method 11 Conclusions 12 Appendix 13 References 20 ILLUSTRATIONS 1. Simplified drawing of modified CEC 24-120A helium leak detector mass spectrometer system 4 2. Schematic of gas flow pattern through stream- switching and gas sampling valves 6 3. Photograph of mass spectrometer system 7 4. Schematic diagram of mass spectrometer electrometer circuit 15 5. Schematic diagram of mass spectrometer ion-source control circuit 16 TABLES 1 . Time-programmed integrator commands for valve sequencing and peak quantization 9 2. Other integration parameters for quantization and plotting of helium peaks 10 3. Comparison of helium analyses obtained using the mass spectrometer and Emerson/Kaplan methods 11 4. List of components and specifications for electro- meter circuit shown in Figure 4 17 5. List of components and specifications for ion-source control circuit shown in Figure 5 18 ABBREVIATIONS AND SYMBOLS USED IN THIS REPORT A ampere "C degree Celsius cm centimeter g gram GQ gigohm h hour He helium ID inside diameter K degree Kelvin kQ kilohm kPa kilopascal MQ megohm \iA microampere yF microfarad liH microhenry jiL microliter mL milliliter mV millivolt, direct current min minute Q ohm OD outside diameter ppm part per million Pa pascal pet percent pF picofarad sec second Vdc volt, direct current Vac volt, alternating current W watt A MASS SPECTROMETER METHOD FOR DETERMINING PERCENT- RANGE HELIUM IN GASEOUS MIXTURES by Philip W. Holland^ ABSTRACT The Bureau of Land Management's Helium Operations office in Amarillo, Texas, has developed a mass spectrometer method to determine percent-range helium in gaseous mixtures. Activated coconut charcoal at liquid nitrogen temperature is used to adsorb components other than helium in the mixture. A modified helium leak detector mass spectrometer is then used to detect the resulting helium "pressure peak." The digitized peak of the unknown sample is compared directly to that of a high-purity helium calibration standard. This method has been demonstrated to be accurate to within +0.1 pet over the concentration range of about 30 to 100 pet helium. ^ U.S. Department of the Interior, Bureau of Land Management, Helium Operations, Amarillo, Texas 79101 ACKNOWLEDGMENT The author expresses his sincere thanks to Mr. Charles A. Seitz, chemist (retired) , Helium Operations, for his assistance in designing and assembling the electronic circuits that are described in the appendix. INTRODUCTION The adsorptive property of activated charcoal was first discovered by Dewar {!)- in 1875. In 1906, Cady and McFarland [2) utilized activated coconut charcoal at liquid air temperature to adsorb components other than helium from a sample of natural gas. Using this technique, they were the first to discover the existence of helium in natural gases. A sample of natural gas they obtained from a well located near Dexter, Kansas, was found to contain approximately 2 pet helium. Beginning in the mid 1930s, the U.S. Bureau of Mines (now defunct) developed several methods which utilized the adsorptive property of liquid-nitrogen-cooled coconut charcoal to determine helium in gaseous samples (3.-5) . These methods required correc- tions for pressure and temperature when measuring the volume of helium that remained after gas adsorption. Frequent calibrations with weighed primary standards (6., 2) were required to obtain accurate results. In 1970, Emerson and Kaplan (8.) developed an improved apparatus and method for determining percent-range helium in natural gases and gaseous mixtures. The accuracy of this method is ±0.04 pet. It was developed out of the need to accurately measure the helium content in crude helium (about 70 pet helium) being purchased from private industry and stored in Bush Dome in the Cliffside gasfield under the Helium Conservation Program (£) . This method is is still in use today to accurately measure the helium content of crude helium being stored for privately owned companies that have contracts with the Bureau of Land Management. The Emerson/Kaplan method simplifies the measurement calcula- tions by eliminating the need to correct the helium volume for temperature and pressure as required by the earlier methods. Activated coconut charcoal maintained at liquid nitrogen tempera- ture (77 K) is used to adsorb all gaseous components except helium and neon, the neon being negligible. The helium pressure resulting from the "injection" of a 7-mL volume of unknown sample is measured using an electronic transducer and then compared to the pressure resulting from the injection of the same volume of pure helium standard. Injections of the sample and standard are performed under the same conditions. With the Emerson/Kaplan method, 20 ^ Underlined numbers in parentheses refer to the list of references at the end of this report. sample analyses can be performed in an 8-h workday. Reactivation of the charcoal in the trap is required after completing 10 sample analyses and is accomplished by allowing the trap to warm to room temperature and then heating it at 200" C for 5 min while under vacuum. The method described in the present report also utilizes a liquid-nitrogen-cooled coconut charcoal trap to adsorb gaseous components from the sample. However, instead of using a pressure transducer to measure the remaining helium, a modified helium leak detector mass spectrometer having a continuously pumped vacuum system is used to detect the helium "pressure peak" as pumpout occurs. The digitized peak resulting from the injection of a 0.1- yL volume of unknown sample is then compared to that of the pure helium standard. Although the mass spectrometer method is not quite as accurate as the Emerson/Kaplan method, it is considered an improvement because 30 sample analyses can be performed in an 8-h workday without the requirement for reactivation of the charcoal adsorbent after every 10 analyses. The mass spectrometer method presently serves as the "back-up" for the Emerson/Kaplan method. MASS SPECTROMETER SYSTEM A schematic diagram of the mass spectrometer system is shown in Figure 1. The system consists of a modified Consolidated Electrodynamics Corporation^^ model 24-120A helium leak detector mass spectrometer, an inlet system utilizing two chromatographic valves, and a liquid-nitrogen-cooled charcoal trap. A Hewlett Packard model 3390A programmable reporting integrator and model 19400A event-control module are used to automate valve switching and to quantify electrometer output. The essential components of the inlet system shown in Figure 1 include the pure helium standard inlet port (A) , sample inlet port (B) , rotameter (C) , stream-switching valve (1), sample injection valve (2), and air-switching solenoid valves (4, 5, and 6) . Inlet ports A and B are Cajon Ultra-Torr male connectors with Viton 0-ring seals. The helium standard and sample gas are admitted to the ports via 0.11-cm-ID by 120-cm-long stainless steel lines. Valve 1 is a Bendix model C-4, 8-port, sliding-piston-type chromatographic valve with Buna-N 0-ring seals. Valve 2 is a Valco model ACI4WM.1, 4-port, rotor-type chromatographic valve with a 0 . l-yL-capacity internal sample chamber. The rotor sealing material is Valcon M. The valves are actuated by compressed air (170 kPa) supplied through the three-way solenoid valves 4, 5, and 6 (Allied Control, model 31382). Solenoid valve 7 is used to divert gas flow from the sample valve prior to sample injection, ^ Reference to specific manufacturers and tradenames does not constitute endorsement by the U.S. Department of the Interior. I o-^ ^ 5 o > o ^ ;u8A X|ddns jp passajdujoD ox- 0) o 0) a CL-1-' k- o Q- O CO ^-C 3- o o ^ ^ ^ c Q. E Q. f— k— M^ t5E-2Y§-o:2 3^ooEa .EcOCtIO 000>^LiJ^ Q-Q mOQ ULl-OX — ^ ^ C cn o o o a. D o c-i I ;o(N pjDpUDl^S 8H 9Jnd E >«. M k- a> ■^ v E o k- "o o Q. OT OT M O E o "o a> "« T3 o _© E < o CM T CM O UJ O ■o ■o o E c *i o 0) a E In 9|dUJDS cn 00 O li. thereby stopping gas flow through the sample chamber and allowing the gas pressure in the chamber to "bleed" to atmospheric. The gas flow pattern through valves 1 and 2 is shown in detail in Figure 2 . Valve sequencing and switching are accomplished using the programmable integrator and event-control module. The sequencing of the valves' operations provides for a staridard-sample-standard series of analyses. The temperature of valves 1 and 2 is allowed to "float" with the ambient temperature; however, their rate of temperature change is minimized by insulating them with a 10-cm- thick layer of glass wool. Measurement of the valve's temperature drift after instrument warmup showed the change to be less than 0.2" C/h. Since the standard-sample-standard analysis series is completed in 12 min, the temperature of the valves is essentially constant during this period. The mass spectrometer is connected to the sample inlet system through charcoal trap E (Figure 1) . The trap is a 0.64-cm-OD (0.10-cm wall) by 56-cm-long stainless steel U-tube with a 0,95-cm- OD (0.10-cm wall) by 5-cm-long "bulb" about 3 cm from the base. The "bulb" contains approximately 2 g of 40/60 mesh activated charcoal (Alltech Associates) . The charcoal is held in place with stainless steel wool packing. The mass spectrometer itself is a 1-cm radius, 180% permanent magnet instrument tuned for mass 4. The ion source temperature is regulated at 75.0±0.1'" C using an external 50-W mantle heater (Briscoe Manufacturing) and a laboratory-built proportional temperature controller (10.). The mass spectrometer's original electrometer and ion-source control circuits were replaced with the laboratory-built, solid-state circuits that are described in the appendix. These circuits were installed to improve the overall stability of the instrument. Helium detection with the mass spectrometer is performed while the ion source is being pumped by the vacuum system (dynamic mode) ; therefore, precise control of the pumping speed is essen- tial. To achieve this control, the line voltage supplied to the diffusion pump heating element is regulated at 105±0.01 Vac using a Sorensen model 1001 voltage regulator. The 0 . 1 6-cm-diameter orifice installed between the mass spectrometer's cold trap and diffusion pump intake (Figure 1) results in a reduced pumpout rate for helium, which produces a more symmetrical helium "pressure peak." The improved peak shape results in a more consistent start- of-peak detection by the integrator. The signal heights of the "pressure peaks" are measured, digitized, and recorded by the integrator . A photograph of the mass spectrometer system is shown in Figure 3. 100X Helium In Sample In Air On ' crr";irr: To rotameta r(p X Plugged Valve 2 To Charcoal trap and M.S. Valve 1 Valve 7 100X Helium In Sample In Air On To rotametej ^ \^ Plugged Valve 2 To Charcoal trap and M.S. Vent Valve 1 100X Helium In Sompje In Air Off tlll-illl] J J C" Valve 1 To rota mete r(p /■ Plugged Valve 2 To Charcoal trap and M.S. Valve 7 100X Helium In Sompje In Air Off -H- J J C" Valve 1 To rotameta ^ Xi Plugged Valve 2 To Charcoal trap and M.S. FIGURE 2. - Schematic of gas flow pattern through stream-switching and gas-sampling valves. A, Purging sample chamber with helium standard; B, Expansion of helium standard; C, Purging sample chamber with sample gas; D, Expansion of sample gas. (Num- bers at valve ports correspond to the manufacturer's numbering of ports. (/) l- (D "5 E o 0) CL V) Vi o Q. O i_ D) _o "o JZ Q- UJ O EXPERIMENTAL PROCEDURES Instrument Preparation The procedures used for startup of the mass spectrometer were as follows. With charcoal trap E connected as shown in Figure 1, valve 3 was closed and power to vacuum pump J and diffusion pump K was switched on. After a 15-min period to allow the diffusion pump to reach its operating temperature, vacuum gauge G was switched on. Cold trap F was then filled (5 cm from top) with liquid nitrogen, and valve 3 was opened to evacuate the charcoal trap. When the pressure (as indicated by G) was below 0.01 Pa, power to ion source H and temperature controller M was switched on. The ionizing current and accelerator voltage of the ion source were then set at 25 pA and 70 Vdc, respectively. Power to vacuum gauge G was then switched off, and the instrument was allowed 1 h for temperature stabilization . During the 1-h stabilization period, the charcoal in trap E was reactivated by heating it while under vacuum. The procedure was as follows. With valve 3 open, the the charcoal-filled "bulb" of the trap was heated at 200"' C for 5 min using a 50-W mantle heater (Briscoe Manufacturing) . The temperature of the heater was manually controlled using a variable autotransformer . After the 5- min bakeout was completed, the heater was removed and the trap allowed to cool to room temperature. The liquid nitrogen filled dewar was then raised so that the liquid level was about 5 cm above the level of the charcoal. After the 1-h stabilization period was completed, the charcoal was conditioned with 12 injections of crude helium (about 70 pet helium and 30 pet nitrogen). The conditioning injections were performed at the rate of three injections per 12-min period, the same rate at which the standard-sample-standard series is performed when conducting sample analyses. Analysis of Samples The flow of the helium calibration standard and the sample to be measured was adjusted to between 10 and 25 mL/min by opening valves 10 and 8 and using a hand-held rotameter to monitor the flow rate. With the standard and sample supply lines connected to the inlet ports as shown in Figure 1, a "Start" command was keyed into the integrator to initiate the sequence of integrator commands shown in Table 1. This series of commands was used to set integration parameters and to operate valves 1 and 2 to produce a standard-sample-standard analysis sequence. Valve 7 was used to stop the flow of gas through the sample valve chamber about 3 sec before injection occurred. Thus, the gas sample in the chamber was at atmospheric pressure when the injection was performed. The integration parameters that remain constant throughout the sequence are given in Table 2. TABLE 1. - Time-programmed integrator commands for valve sequencing and peak quantization. Time- Programmed Command* Time of Execution, min Action of Executed Command' START EXT 5 EXT 6 INTG 0 INTG 5 EXT 8 EXT -8 EXT 7 EXT -7 EXT -5 EXT -6 EXT 6 INTG 0 INTG 5 EXT 8 EXT -8 EXT 7 EXT -7 EXT 5 EXT -6 EXT 6 0.00 0.01 0.47 0.50 0.51 0.52 0.92 0.94 0.96 0.98 1.00 4.47 4.50 4.51 4.52 4.92 4.94 4.96 4.98 5.00 8.47 Sequence of commands is begun. Valve 1 is actuated to allow helium standard flow to valve 2. Helium standard flow to valve 2 is stopped by activation of valve 7. Present baseline is immediately as baseline reference point. Baseline is extended horizontally from last declared reference point. Valve 2 is actuated to admit helium standard to mass spectrometer. Air pressure for actuation of valve 2 is relieved. Valve 2 is returned to purge posi- tion . Air pressure for returning valve 2 to purge position is relieved. Valve 1 is returned to enable sample flow to be established to valve 2. Sample flow to valve 2 is started by deactivation of valve 7. Sample flow to valve 2 is stopped by activation of valve 7. Present baseline is immediately declared as baseline reference point . Baseline is extended horizontally from last declared reference point. Valve 2 is actuated to admit sample to mass spectrometer. Air pressure for actuation of valve 2 is relieved. Valve 2 is returned to purge posi- tion. Air pressure for returning valve 2 to purge position is relieved, helium standard flow to be re-established to valve 2. Helium standard flow to valve 2 is re-established by deactivation of valve 7 . Helium standard flow to valve 2 is stopped by activation of valve 7. 10 ;Continuation of Table 1) INTG 0 INTG 5 EXT 8 EXT -8 EXT 7 EXT -7 EXT -6 STOP 8.50 8.51 8.52 8.92 8.94 8.96 8.98 12.00 Present baseline is immediately declared as baseline reference point . Baseline is extended horizontally from last declared reference point. Valve 2 is actuated to admit helium standard to mass spectrometer. Air pressure for actuation of valve 2 is relieved. Valve 2 is returned to purge posi- tion. Air pressure for returning valve 2 to purge position is relieved. Helium standard flow to valve 2 is re-established by deactivation of valve 7 . Sequence is terminated and digitized peak heights are printed out. Integrator commands are for a Hewlett Packard model 3390A reporting integrator. References are to valves 1, 2, and 7 in Figure 2. TABLE 2. - Other integration parameters for quantization and plotting of helium peaks. Integration Parameter' Description of Parameter Parameter Setting PK WD THRSH ATT 2t CHT SP Peak width - time width of peak at half height (min) Threshold - discrimination level for eliminating signal changes regarded as noise (value entered is integer power of 2) Attenuation - plot height scale (value entered is integer power of 2) Chart speed - plot width scale (cm/min) 0.01 3 0.5 The integration parameters are for a Hewlett Packard model 3390A reporting integrator. An "Automate Runs" options for the integrator was used to cause the standard-sample-standard analysis sequence to be repeated after each printout of the three peaks acquired during a sequence. The peaks were quantized as height counts (1 height count = 1.25 X 10"" mV) by selecting the "Peak Height" mode for integration. 11 The liquid nitrogen level surrounding the charcoal trap was adjusted to the same point at the beginning of each standard- sample-standard analysis sequence by refilling the dewar to overflowing. The liquid level in the dewar drops approximately 2 cm during the 12-min period required for completion of the analysis sequence . ACCURACY OF METHOD The accuracy of the method was determined by analyzing a group of 15 gas samples containing from 29.15 to 95.53 pet helium. The samples had previously been analyzed using the Emerson/Kaplan method. A comparison of the analysis results is given in Table 3. A sample gas (No. 1) containing almost 5 pet hydrogen could be analyzed without detectable interference from the hydrogen impurity. TABLE 3. - Comparison of helium analyses obtained using the mass spectrometer and Emerson/Kaplan methods. Sample Number Mass Spectrometer Emerson/Kaplan and Description Method, pet He Method, pet He ~T"! Helium standard: 86. 61 + 0. 03 86.50 86.50 pet helium, 4.73 pet hydrogen, 4.37 pet methane, and 4.40 pet argon 2. Helium upgrader 95.43+0.11 95.53 product 3. Helium standard: 29.20+0.05 29.15 29.15 pet helium, 30.77 pet nitrogen, and 40.08 pet methane 4. Crude helium 64.07+0.04 64.08 5. Crude helium 70.52+0.03 70.56 6. Crude helium 73.79+0.05 73.81 7. Crude helium 72.49+0.09 72.47 8. Crude helium 70.48+0.11 70.46 9. Crude helium 71.00+0.05 70.98 10. Crude helium 69.70±0.06 69.79 11. Crude helium 69.90+0.11 69.86 12. Crude helium 68.56+0.02 68.60 13. Crude helium 68.30+0.02 68.33 14. Crude helium 64.22+0.04 64.21 15. Crude helium 70.42±0.07 70.38 The mass spectrometer method results are the means for three successive analyses, and the values for the Emerson/Kaplan method are the means obtained for two successive analyses. The mass spectrometer method results were found to agree with the Emer- 12 son/Kaplan method results within the analytical precision of about + 0.1 pet. The accuracy of the method is considered to be the same as the precision since pure helium is used as the calibration standard. The method was found to be linear over the investigated range of 29.15 to 95.53 pet helium. CONCLUSIONS The newly devised mass spectrometer method described in this report is useful for determining helium in the 30- to 100-pct range. The method provides additional analytical capability for determining the helium content of pipeline crude helium (about 70 pet helium) that enters and leaves the Bureau of Land Management's crude helium storage reservoir located near Amarillo, Texas. The method is also useful for certifying percent-range helium standards that are prepared in the laboratory. The accuracy of the method is within ±0.1 pet (absolute) . The presence of approximately 5 pet hydrogen in a test gas sample had no detectable effect on the helium result. Since such a small volume of sample gas (0.1 laL) is admitted to the liquid-nitrogen- cooled charcoal adsorbent trap at each injection, regeneration of the adsorbent is not required during an 8-h workday. The method was demonstrated to be linear over the investigated range of 29.15 to 95.53 pet helium. Sample analyses can be performed at the rate of 1 analysis per 12-min period. 13 APPENDIX The circuits that were used to replace the original electro- meter and ion-source control circuits in the CEC 24-120A helium leak detector mass spectrometer are diagrammed in Figures 4 and 5, respectively. The circuits were assembled using commercially available components. Lists of components and their specifica- tions for the electrometer and ion-source control circuits are given in Tables 4 and 5, respectively. The electrometer circuit (Figure 4) utilizes an operational amplifier (A) for ion current amplification. The amplifier is used in a picoampere current-to-voltage converter inverting configura- tion. The feedback resistance (RJ value of 500 GQ was selected to achieve an output of about 0.5 Vdc with a 100 pet helium sample. Acceptable outputs for low-percent helium samples can be achieved by selecting values for R^ that are greater than 500 GQ. The amplifier-zeroing portion of the circuit is composed of resistors R,, R^, R5, Rg, and R 9, and potentiometer P^, and capaci- tors C, and C3. Zero drift of the amplifier is minimized by using a capacitor having a low temperature coefficient for C2 . Resistor R2 is used to limit the flow of current to the noninverting input (pin 3) of the amplifier if C2 is fully charged when the circuit is initially powered up. Diodes D^ and D2 and capacitors C^ and C5 protect the amplifier from voltage spikes. Attenuation of the output signal is accomplished using the voltage divider consisting of resistors Rg and R7, potentiometer P| , and switch S. For high- percent helium samples, Pj is adjusted to 80 pet of its maximum resistance value and S is set at the "X 10" position. The portion of the circuit shown enclosed by dotted lines in Figure 4 was installed on the electrometer circuit board supplied by the instrument manufacturer. The circuit board is housed in a 6 X 9 X 18 cm metal case that is located near the mass spectrome- ter's ion source (Figure 1) . To further minimize drift caused by temperature changes, the circuit board housing was insulated using a 2 . 5-cm-thick layer of foam rubber sheeting. The ion-source control circuit (Figure 5) was designed to provide a constant ionizing current by regulating direct current through the mass spectrometer filament. The circuit provides adjustment and control of the ionizing current up to 150 ]iA; however, the upper limit of ionizing current can be extended by using resistances of less than 50 kQ for resistor R^ . The circuit utilizes an operational amplifier (A) and two transistors (Q^ and Q2) for control of current through the mass spectrometer filament. Electron flow from the filament to the anode (ionizing current) causes a sensing voltage to be developed across R4 and at pin 5 (noninverting input) of the amplifier. The difference between the voltage at pin 5 and the set-point voltage supplied from the wiper of potentiometer P^ at pin 4 is amplified. The output of the amplifier at pin 10 controls controls the current through transistor Qj and, likewise, through transistor Q, and the filament. The control of current through the filament regulates 14 the temperature of the filament and the rate at which electrons are emitted. Thus, the voltage developed at pin 5 as a result of the electron flow from the filament to the anode and through resistor R4 occurs to such an extent that the set point voltage at pin 4 is equaled. The circuit is phased in such a manner that a random increase in ionizing current will cause the sensing voltage at pin 5 of the amplifier to become more negative relative to circuit ground. When this occurs, the output from the amplifier becomes less positive, thereby causing transistors Qi and Q2 to be less conductive. As transistor Q2 becomes less conductive, current through the filament is reduced, thereby reducing the temperature of the filament. Thus, the ionizing current is reduced toward the control set point. The converse of the above description occurs when there is a random decrease in ionizing current. By adjusting potentiometer P^, a different ionizing current can be established. Transistor Qj was selected for use in the circuit based on its ability to match the relatively low current output of the amplifier and to provide adequate current for driving Q^ . The current gain for Qi as used in the circuit is calculated to be 135. The heat sink used with Qj has a maximum temperature rise of 25"' C/W. Transistor Q. was selected for its 150-W power rating. This rating provides an adequate safety factor when considering that approximately 11 W is dissipated by Q-. when a 4-A filament current flows through it. As used in the circuit, the current gain of Q2 is calculated to be 60, The heat sink for Qo has a maximum temperature rise of 0.5"-' C/W. Diode Dj was installed to protect the amplifier if the ion- source anode is shorted to ground. Diodes D^ and D, were installed to protect the amplifier from voltage spikes that might inadver- tently be picked up at the output. Power supplies PSj, PS .' PS 3 , and PS^ are used to furnish voltages to the ion-source anode, filament, accelerator, and the operational amplifier, respectively. The accelerator voltage is set at 70 Vdc above circuit ground using potentiometer P2 . The pilot light was installed in parallel with the filament to indicate filament operation. The light glows dimly under control conditions but glows brightly when the filament is open. The microampere meter indicates the value of the ionizing current. 15 o 0) -*- 0) E o "o _a) (I) i> E o "o 0) Q. W V) V) O E E D \- (I> o 00 a: Z) o c o u 16 in (M 'I* < to a. < - O ~ 8 of 2 ■^VW ■Ayyv .^Vv^V O o in J' O c < O 1^ 5 1 T wl a> jcl o o ^ -Q <-> — 0) V Q. P «" ^ . o •2 w (rt o c 2.2 (0 _ _ Q. ». *> •« 2 .. O - O 3 i: «/) O) k. .^ u5 c o « » ; O c ,- K q: a o Q. £ Q. en _j o q: Q. < a. D " " c o o .2 o ■" ^ o w O Q CL £ 5 O CL .. E O Q Ol _l sHi- or C o c o O O O (0 I c o 0) E o a. V) Vi U) D E E o 1- D O "o E a> O CO in ui =) o c\j 17 TABLE 4, - List of components and specifications for electrometer circuit shown in Figure 4. Component Specifications A operational amplifier Ci capacitor C2 capacitor C3 capacitor C4 capacitor C5 capacitor Dj diode D2 diode Pi potentiometer P2 potentiometer Ri resistor R2 resistor R3 resistor R4 resistor R5 resistor Re resistor R7 resistor Rs resistor R9 resistor s switch PS power supply Analog Devices model AD515LH 5 pF, 25 Vdc, electrolytic type 0.47 \iF, 50 Vdc, metalized- polycarbonate type with low temper- ature coefficient 0.1 \iF, 25 Vdc, ceramic type 2.2 ]iF, 25 Vdc, electrolytic type 2.2 jjiF, 25 Vdc, electrolytic type type IN4002 type IN4002 2 kQ, 10-turn, temperature coefficient ±20 ppm/"C 10 kQ, 10-turn, temperature coefficient ±20 ppm/^'C 500 GQ, glass-encapsulated, Victoreen Instruments, type RX-1 10 kQ, 0.25 W 3.9 MQ, 0.25 W 1.2 kQ, 0.25 W 1.2 kQ, 0.25 W 18 kQ, 0.2 5 W 180 kQ, 0.25 W 4.7 kQ, 0.25 W 4.7 kQ, 0.25 W single-pole, three-position dual, +15 Vdc and -15 Vdc, Calex Manufacturing Co., model 22-100 18 TABLE 5. - List of components and specifications for ion-source control circuit shown in Figure 5. Component Specifications A operational amplifier Ci capacitor C2 capacitor C3 capacitor C4 capacitor C5 capacitor Ce capacitor C7 capacitor Di diode D2 diode D3 diode D4 diode L inductor M meter Pi potentiometer P2 potentiometer PL pilot light PSj power supply PS2 power supply PS3 power supply Precision Monolithics, model OP-07-EY 2.2 ]iF, 25 Vdc, electrolytic type 0.047 liF, 25 Vdc, ceramic type 1 ]iF, 25 Vdc, tantalum type 1 \iF, 25 Vdc, tantalum type 0.1 \iF, 25 Vdc, ceramic type 5 ]iF, 200 Vdc, electrolytic type 0.01 iJiF, 200 Vdc, ceramic type type IN4004, low-leakage tested type IN4002 type IN4002 type IN4002 10 uH 0-200 uA 2 kQ, 10-turn, temperature coeffi- cient ±2 0 ppm/°C 100 kQ, 10-turn, temperature coefficient +20 ppm/"C incandescent, no. 47 adjustable, 125-175 Vdc, Lambda Electronics, model LDS-Y-150 adjustable, 5-9 Vdc, Lambda Electronic, model LDS-W-01 adjustable, 125-17.5 Vdc, Lambda Electronics, model LDS-Y-150 19 PS^ power supply Qj transistor Q2 R. transistor Rj resistor R2 resistor resistor R. resistor R5 resistor Re resistor Rv resistor Rs resistor R9 resistor Rio resistor Rn resistor R12 resistor dual, +15 Vdc and -15 Vdc, Calex Manufacturing Co., model 22-100 NPN, type 2N2219 NPN, type 2N3716 2 kQ, 0.25 W, temperature coeffi- cient ±8 ppm/^'C 1 kQ, 0.25 W, temperature coeffi- cient ±8 ppm/°C 4 kQ, 5 W 50 kQ, 0.25 W, temperature coeffi- cient ±8 ppm/'^C 100 Q, 0.25 W 4.7 kQ, 0.25 W 470 Q, 0.25 W 15 Q, 5 W 0.5 Q, 10 W 1 kQ, 0.25 W 100 kQ, 0.25 W, wire-wound type 100 kQ, 0.25 W, wire-wound type 20 REFERENCES (1) Dewar, J. Charcoal Vacua. Nature (London), v. 12, July 15, 1875, pp. 217-218. (2) Cady, H.P., and D.F. McFarland. The Occurrence of Helium in Natural Gas and the Composition of Natural Gas. J. Amer. Chem. Soc, v. 29, no. 11, November 1907, pp. 1523-1536. (3) Anderson, C.C. An Apparatus and Method for the Determina-tion of Helium in Natural Gas. U.S. Bur. of Mines IC 6796, 1934, 11 p. (4) Frost, E.M. Improved Apparatus and Procedure for the Determi- nation of Helium in Natural Gas. U.S. Bur. of Mines RI 3899, 1946, 16 p. (5) Frost, E.M,, C.G. Kirkland, and D.E. Emerson. An Apparatus for Determining the Helium Content of Gas Mixtures. U.S. Bur. of Mines RI 6545, 1964, 18 p. (6) Miller, J.E., A.J. Carroll, and D.E. Emerson. Preparation of Primary Standard Gas Mixtures for Analytical Instruments. U.S. Bur. of Mines RI 6674, 1965, 10 p. (7) Loya, E.W., C.A. Seitz, and D.E. Emerson. Gravimetric Preparation of Primary Standard Gas Mixtures in the Parts-Per- Trillion Range. U.S. Bur. of Mines RI 8643, 1982,4 p. (8) Emerson, D.E., and R.L. Kaplan. Method and Apparatus for Determining Helium Content of Gas Mixtures. J. Amer. Chem. Soc. , V. 42, no. 14, December 1970, pp. 1746-1748. (9) Chemical Week. Relieving the Helium Bind. September 1961, pp. 57-59. (10) Lucich, G.M., and P.W. Holland. A Proportional Temperature Controller With Automatic Shutoff. U.S. Bur. of Mines RI 8423, 1980, 8 p. #-^^ .^^ ^ * U.S. GFO 1996: 573-016/40511 REPORT DOCUMENTATION PAGE Form Approved OMBNo. 0704-0188 Public reporting burden for this collection of inlormalion is estimated to average 1 hour per response, including the lime tor reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports. 1 2 1 5 Jefferson Davis Highway. Suite 1204, Arlington. VA 22202-4302. and to the Office of Management and Budget. Paperwork Reduction Project (0704-0188). Washington. DC 20503, 1. AGENCY USE ONLY CLeave Wan/(j 2. REPORT DATE November 1996 3. REPORT TYPE AND DATES COVERED Final 4. TITLE AND SUBTITLE A Mass Spectrometer Method for Determining Percent-Range Helium in Gaseous Mixtures 6. AUTHOR(S) Philip W. Holland 5. FUNDING NUMBERS 7. PERFORMING ORGANIZATION NAME{S) AND ADDRESS(ES) U.S. Department of the Interior Bureau of Land Management - Helium Operations 801 South Fillmore, Suite 500 Amarillo, Texas 79101-3545 8. PERFORMING ORGANIZATION REPORT NUMBER BLM/HE/ST-97/00 1 -1-3700 ID ADDRESS(ES) O I a) a> U 0) 0) Ou in P , CO 6 a.' d CO <3 u u O REPORT DOCUMENTATION PAGE Form Approved OMBNo. 0704-0188 Public reporting burden lor this collection of inlormation is estimated to average 1 hour per response, including the time lor reviewing inslnjctions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect ol this collection ol information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway. Suite 1204. Arlington. VA 22202-4302. and to the Office of l^anagement and Budget. Paperwork Reduction Project (0704-0188). Washington. DC 20503 1. AGENCY USE ONLY fLeai'e Wan/t; 2. REPORT DATE November 1996 3. REPORT TYPE AND DATES COVERED Final 4. TITLE AND SUBTITLE A Mass Spectrometer Method for Determining Percent-Range Helium in Gaseous Mixtures 6. AUTHOR(S) Philip W. Holland 5. FUNDING NUMBERS 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) U.S. Department of the Interior Bureau of Land Management — Helium Operations 801 South Fillmore, Suite 500 Amarillo, Texas 79101-3545 8. PERFORMING ORGANIZATION REPORT NUMBER BLM/HE/ST-97/00 1 +3700 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITORING AGENCY REPORT NUMBER 11. SUPPLEMENTARY NOTES 12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE 13. ABSTRACT (Maximum 200 words) The Bureau of Land Management's Helium Operations office has developed a mass spectrometer method to determine percent-range helium in gaseous mixtures. Acti- vated coconut charcoal at liquid nitrogen temperature is used to adsorb components other than helium in the mixture. A modified helium leak detector mass spectrometer is then used to detect the resulting helium"pressure peak." The digitized peak of the unknown sample is compared directly to that of a high-purity helium calibration standard. This method has been demonstrated to be accurate to within plus or minus 0.1 percent over the concentration range of about 30 to 100 percent helium. 14. SUBJECT TERMS Helium Mass spectrometer Gaseous mixtures Percent-range helium 15. NUMBER OF PAGES 20 16. PRICE CODE 17. SECURITY CLASSIFICATION OF REPORT Unclassified 18. SECURITY CLASSIFICATION OF THIS PAGE Unclassified 19. SECURITY CLASSIFICATION OF ABSTRACT Unclassified 20. LIMITATION OF ABSTRACT UL NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89) Prescnbed by ANSI Std Z39-18 298-102 m > 5q O U I m c= m £/> CO O O O > I— DO C CO 2 m (f) (/) > 00 I CD C 3 o 0) o 0 E' 3 c -^ (D c CO o p c O o CD ■D :d 3" ■D "* 03 (D Tl (D 1— 3. X S 0) 3 3 3 o — T 1— »■ o' 3 a 0 CD Q W 0) 03 O — h O CO 3" _x C_ (Q (D CO CJl (D 3 (D 3 Ul O D -^ O o" o TJ ■D O J3 C Z H ■< m O < m I]